1. Field of the Invention
The production of hydrochloric acid by destruction of chlorinated hydrocarbons yields a product that is coloured yellow, caused by, among other things, the presence of iron, free bromine and free chlorine. Such an acid has small industrial application and is of low value. To increase the value it is therefore necessary to remove this colour from the acid in a simple and cheap way.
2. Description of the Prior Art
In earlier known methods to remove these types of compounds from hydrochloric acid. U.S. Pat. No. 4,349,525 describes a method for purification of hydrochloric acid that is produced by a reaction between alkali chloride and sulfuric acid. It was found that the colour was caused by Br.sub.2 and that simultaneous removal of SO.sub.2 also resulted in a decrease in the colour level. According to this patent, the acid is purified by stripping with inert gas and oxygen. A colourless acid was obtained. However, this is an expensive process as a stripping tower and the supply of a sufficient amount of inert gas/oxygen is needed.
European patent application No. 0 506 050 discloses a method for the removal of fluorine, bromine, iodine and their hydrogen compounds, from hydrochloric acid. This is carried out by a first removal of HF and fluorides by the addition of a stoichlometric excess of a chlorine salt that can be dissolved, which leads to precipitation of their fluoride compounds. Thereafter the acid is distilled. To remove Br.sub.2, I, bromides and iodides, chlorine is added in such amounts that elementary bromine or iodine is formed and thereafter is removed by stripping with water vapor. This is a very comprehensive and expensive process step.